Assume that in a world with current levels of technology much like our own, a developed country with at least tens of millions of people and more than a city-state sized territory, decided that all active duty military personnel needed to be women. Feel free to pick one (e.g. Canada or France) if you feel this is necessary to provide an answer.

The reason for this isn't terrible important for these purposes - maybe there is a religious or philosophical reason; maybe it is motivated by a traumatic mass-rape experience in a previous war; maybe a highly effective biological weapon that affects only men has been developed - simply accept this as a premise.

Assuming that other military forces in the world remain unchanged, how would this women's only military force be designed differently from existing military forces? How would its strategies and tactics differ?

What military capabilities would be little changed and which ones would be greater or weaker?

Answers need not be comprehensive. Selected observations responsive to these questions would be appreciated.

$\begingroup$Why should they differ in any way?$\endgroup$
– dot_Sp0TMay 24 '17 at 15:45

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$\begingroup$@dot_Sp0T If you can articulate a reason why they would not, this would be an acceptable answer. Given that there are no historical examples of such a military, however, and only one legendary one (the Amazons) which involved a very different technology level, this isn't a foregone conclusion one way or the other.$\endgroup$
– ohwillekeMay 24 '17 at 15:47

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$\begingroup$If you're going to vote to close a question, make sure to leave a comment explaining why. I cannot for the life of me understand why people think this question is primarily opinion-based. It could be tagged hard-science and get valid answers with the amount of research that has been poured into gender differences. I could potentially understand too broad but notprimarily opinion-based.$\endgroup$
– AzuaronMay 25 '17 at 18:10

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$\begingroup$After reading this entire page I am incredibly surprised at how little intelligent men think of women. I read comments about how women are weaker, slower, have less stamina stated as if were fact without any proof to back it up. And no statements of them being intelligent enough to be military leaders. Bottom line: the ONLY difference between men and women is we're muscularly stronger and on average taller. Modern warfare does not have anything to do with that since we are no longer swinging swords. A woman can shoot a gun, drive a tank, fly a jet fighter, and guide a missle as well as a man.$\endgroup$
– LenFeb 8 '18 at 6:54

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$\begingroup$@Len I'm inclined to agree with you. The physical differences wouldn't be huge and would lead to minor adjustments, I think (based on forces with high levels of women like Israel, the Kurds, and N. Korea). And, while I don't like IQ would be different, I do think that the differences in psychology would be pretty profound (90%-95% of major violent crime is male in every society on Earth and that reflects psychological differences that would play out in how decisions are made in military settings).$\endgroup$
– ohwillekeFeb 8 '18 at 22:05

13 Answers
13

Over the last few decades female participation in the world's armed forces has increased markedly. While initially allocated to supporting roles, some have sought to integrate them into combat roles and even special forces. Recently Norway created the Hunter Troop (female special forces team), and the US Army Rangers accepted its first female recruits. Not to mention Yazidi and Kurdish women volunteering with the Peshmerga to get revenge on ISIL and protect their families.

What's interesting to note however is how the debate is different between the Anglosphere and Israel. In the former it is often said that the decision to allow more women into the military, and specifically combat roles, is an imposition by idealistic political masters.

One senior British officer went so far as saying that allowing women into British Army combat roles was: "foolish move" which would be "paid for in blood" and was by "politicians desperate to seem progressive, feminist zealots, and ideologues hell bent on opportunity without exception".

On the other hand... worth noting that US Generals are calling obesity a threat to national security. Clearly when a third of young Americas are too fat to fight, the question of women's eligibility for combat roles is put in realistic perspective.

Meanwhile in Israel the situation is different. Israel relies upon conscription, and so 65% of Israeli women have served in the military. All women are conscripted, but of those 25% opt out for religious reasons, and 10% are not fit to serve. In 2011 33% of all IDF soldiers and 51% of officers were women.

In 2007 the Segev Committee report was commissioned by Major General Elazar Stern, Head of Manpower Directorate. The report recommended opening all military roles to women. It was given to the IDF General Staff, receiving the blessing of the then Chief-of-Staff. It concluded that length of service and promotion had been based mostly on gender, and that:

"This is an archaic model that causes under-utilization of the
resources ... of half of Israeli society, and closes off many
opportunities, both during service and for integrating into society
after service"

Perhaps the problem isn't that women in combat is a bad idea, or that there is evidence against it, but that the USA and UK are spoilt. They've never needed to deploy their entire population to fight for their survival like Israel has.

Modern warfare is far removed from the melee of the medieval era which relied upon tall strong men. There are simply more important factors these days, and just because the enemy may be on average larger doesn't guarantee them victory in melee. Especially since many martial arts allow one to use the attacker's size against them. If these concerns were salient it would be unlikely that a military as ever-ready as the IDF would have so eagerly embraced ending restrictions on combat roles for women.

It's also worth remembering that the average Vietnamese man is as tall as the average American woman. Was that the biggest factor in the Vietnam War?

Weapons and tactics have evolved to minimise risks and allow soldiers to use firearms in close quarters if need be. In the second world war battle rifles were often huge unwieldy things. Not so nowadays with SMGs and the like; ideal for urban warfare. Ultimately technology has allowed us to create physical distance with the enemy, and that diminishes any bonus men have for being big and strong. Does it matter if a pilot is a man or woman? A driver? A sniper? How much of modern warfare is melee, and how many times is this the turning point in a war?

Clearly having a high proportion of women isn't the biggest factor in IDF planning. Other factors, like geography, training, hardware, and the enemy, are far more important. At the very least, a female army is unlikely to be anywhere near as prolific a sexual offender as the Red Army was during the fight to Berlin.

In 2007 the UN deployed a unit of Indian women in Liberia as peacekeepers. One concern was that units of male soldiers would be regarded with suspicion by populations which had been terrorised by sexual violence during the conflict. The deployment was considered a great success.

Immediate Effects

The first thing the new military will have to deal with is the enormous loss of military experience at all levels.

Going by US numbers, you've just lost around 85% of your people. The balance between enlisted personnel and officer ranks is roughly equal, but the loss is worst at the highest levels of the officer corps, where you've lost 93% of your institutional experience, as well as nearly ALL of your front-line combat experience. The people who've been out there, making mistakes and learning from them for years, are suddenly gone, and unable to pass those lessons on to the next generation.

The effect is going to be a lot like the infamous Red Army Purge conducted by Stalin; exactly how that affected Soviet performance in the early part of the Great Patriotic War is still being debated, but it's generally agreed that the inexperience of the commanders and officers contributed a lot to their early defeats by the Germans.

To cope with this, one can imagine a need to recruit very aggressively, and promote rapidly, as well as a focus on education for high-ranked officers. Sun-Tzu, Vegetius, and other classics are going to become bestsellers, as are other war memoirs. With any luck, the all-female force will have a chance to get some combat experience in skirmishes or peacekeeping missions before they need to fight for their lives.

Compensation

Biologically speaking, women on average are not as strong as men. This is just a fact. Training and exercise can overcome a woman's naturally lower strength, but she'll need to train longer and harder than a man to get the same results. In any kind of physical fight, the female force is going to be at an overall disadvantage, whether it's fought with rifles or bayonets.

The army should therefore institute very strict daily PT requirements for their infantry, and weed out anyone who can't meet them. They're basically going to be the British Army on steroids - a small infantry force, but all dedicated, highly trained professionals.

Since it's going to be harder to maintain infantry, a greater emphasis on battlefield mobility, infantry fighting vehicles, armoured transports, and armour is very likely. That in turn is going to lead to a very strong emphasis on logistics.

You're going to end up with a relatively small, highly trained, highly disciplined, professional force. They'll use a lot of armoured vehicles, but they'll be inexperienced at first, and will need to be constantly training and learning. An environment where a soldier can speak frankly to her superiors will be essential, as will promotion by merit.

Tactics

So, you've got a small army. Not the end of the world. Your best bet will be short, sharp action, bringing concentrated force to bear on individual enemy elements. Most of the heavy fighting should be conducted by armoured vehicles like main battle tanks, light tanks/armoured fighting vehicles, air power, etc.

Your infantry forces would be a reactive force, able to move quickly to trouble spots as needed with less difficulty than the main armoured units, and able to perform the many tasks needed of the infantry in a modern war, like building clearance. Each infantry squad would have its own attached Infantry Fighting Vehicle to transport them quickly to trouble spots and provide fire support. The soldiers would deploy from the IFV, use it as cover, and return to it when they were needed elsewhere.

$\begingroup$There is also likely a huge social/political aspect of sending wives and daughters into battle that would probably influence how politicians chose to use the military.$\endgroup$
– StrongBadMay 24 '17 at 20:26

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$\begingroup$Not if those wives and daughters are widows and orphans.$\endgroup$
– Rick RykerMay 24 '17 at 20:31

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$\begingroup$We're assuming a culture that has already decided to go 100% female army. I don't think we can really make any sort of reliable assumptions about the social/political implications.$\endgroup$
– Ben BardenMay 24 '17 at 20:39

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$\begingroup$Physical strength has little use in a modern army, only a few functions still require it.$\endgroup$
– SashaMay 24 '17 at 22:46

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$\begingroup$Between body armor, weapons, ammunition, and other gear, modern US soldiers routinely carry 60-100 pounds of gear. Most healthy adults can lift that much, but carrying it around all day requires a LOT of energy. It would be, proportionately speaking, a much larger percentage of an average woman's weight which would magnify the effect. This army would likely change the nature and length of its missions to lessen the load each individual carried. But to say physical strength doesn't matter to a modern army is not true. Edit: I see this is discussed in more detail in an answer below.$\endgroup$
– JoeMay 24 '17 at 23:07

1 Year

On the one year timescale, your military is going to be dramatically weakened by switching to all women. This is a simple cause and effect relationship. If you suddenly fire about 85% of your employees, and then hire a bunch of new employees, you're going to have a massive brain drain that will hurt, regardless of whether or not these new hires are done along gender lines or not. You will also find you have to lower your standards because there's not going to be a massive body of women who are ready to take on this role. You can only employee so many people on a national scale before you drain the talent pool. This happened post 9/11 with the intelligence agencies, who suddenly demanded a massive number of additional IT personel. The security experts warned that they were trying to hire more people than the talent pool would permit, and they would get lower quality personel as a result. Snowden was one of these new hires from that timeframe.

Other than this, nothing would change on the 1 year timescale. All tactics, strategies, etc. will remain the same. Militaries move slowly. It can take them decades to bring in new technology, long after the commercial culture has adopted them ubiquitously. This, of course, is also a very rational process: their lives literally depend on their stuff working in extreme climates with an enemy military actively trying to break them and end their lives. They would use the tried and true approaches instead.

10 year

In the 10-30yr region, it gets a bit more interesting. This is enough time to really properly train up new talent, and start thinking about a steady state pool of soldiers. This is where I would expect to see the first gender specific adaptations, and I would expect to see them fall along the lines of the typical gender stereotypes. I make this assumption because on this timescale, society hasn't had any time to adapt the gender roles we raise our children to in response to this change in the military. You're still going to have people raised in the same manner. More importantly, the higher up the chain of command, the more traditional people will be because they're the older generation.

I expect to see tactics change to work around lower physical loads but leveraging the differences in how the masculine and feminine mind work. Combat will be directed to where attention to millions of tiny details and multitasking will be more important, because those are things that stereotypically the men in the opposing army aren't so good at. Rule number 1 of combat is to know thyself and know thy enemy -- make the battlefield inhospitable for them, and friendly for you. I would expect to see more fluid approaches in the highest levels of strategy, and fewer directed approaches.

100 year

This is where it gets really interesting. On the timescale of 100 or 200 years, you have substantial time to adjust the gender roles over multiple generations. This, in my opinion, is the open question that is explored by those who push gender limits. Just how much of our gender roles are actually tied to real life practical limits of the sexes versus how much is the culture that we have built around these limits to make them disappear. Its entirely possible that we find women actually aren't the best suiteded for warfare, and we go back to using men. It's entirely possible to find that the physical differences between them matter little compared to the mental effects of gender roles, and a change in gender roles could make women completely suited for warfare. Its also entirely possible that we might find out that some of our gender roles actually affect hormones enough to undo any sex specific physical advantages men have. We really don't know the answers on these timescales. Psychologists and biologists are still actively theorizing here.

100 years is, however, enough time to completely overhaul the tactics of the military. In fact, all militaries will have overhauled their tactics and strategies on this timeframe. 100 years of technical advances is more than enough to make entire military theories obsolete.

$\begingroup$One could argue that the prevalence of men-as-warriors throughout human history is the ultimate case study of the influence of gender on combat ability.$\endgroup$
– PipperChipMay 24 '17 at 19:44

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$\begingroup$@PipperChip I think you are probably right. We only have a few million years of evolution behind it, although with the shift to more and more technologically empowered ways of waging war, it's not as obvious whether that case study is relevant today. However, we do have to remember that the OPs question intentionally handwaves the reason for the shift to female combatants. The rationale behind that might be a valid argument for why the old ways no longer apply.$\endgroup$
– Cort AmmonMay 24 '17 at 20:26

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$\begingroup$@PipperChip The problem is that there's a reproductive advantage to letting men die in war (instead of women): one man can impregnate several women at a time, a single woman cannot have children from multiple men at the same time. This clear evolutionary advantage in who is allowed to die could easily be masking the combat effectiveness differences (if any) between the genders. Beyond that, warfare has changed faster than people have evolved, so who's to say which gender is more effective at modern warfare since a mass-scale female army with modern weaponry has never existed?$\endgroup$
– AzuaronMay 25 '17 at 13:46

$\begingroup$The OP asked for how a women only military would be different not for a discussion on why men are better at it than women. It is presumed that whatever happened happened already and they dealt with it by going to an all female army. Imagine a world were a genetic aberration entered the population which was expressed in men only on their x chromosome and which spread throughout the country's population in a single generation making too difficult to undo. Further image that his genetic aberration caused all men to die by the age of 17 with a standard deviation of 2 years. 98% between 13 and 21.$\endgroup$
– Rick RykerMay 27 '17 at 5:49

$\begingroup$@RickRyker In that scenario, see my answer for what would likely happen on the 1 and 10 year timescales. On the 100 year timescale, it's not very clear, as my answer pointed out.$\endgroup$
– Cort AmmonMay 27 '17 at 20:57

Physical Strength and Endurance

During the Cold War, many countries drafted young men to serve in the armed forces, and later in the reserves. Some were fit, some were less fit, most were able to serve in some capacity.

These days the armed forces are much smaller. A medium-sized country should be able to find a hundred thousand women who are as strong and fit as the average 18-year-old couch potato. Questions of strength will hurt in some roles, like hauling mortar bombs or hand-to-hand combat, but look at the kind of people who got drafted into the infantry as WWII ground on.

Social/Psychological Factors

These are a bit tricky because they might no longer apply as we know them when a country is prepared to go for an all-female army.

One could argue that young men make good enlisted soldiers because they will take stupid risks to impress each other and any females who may be watching. When push comes to shove, soldiers don't die for an abstract ideal, they die to avoid disappointing their comrades. Would the same dynamics develop in a female army? Will they be less macho and more nurturing? Will that make them better or worse soldiers?

I'm assuming that the other countries will not change over. How will a male infantry squad react if they are told to storm a bunker held by female soldiers? Chivalry on the one hand and sexual violence on the other hand have always been part of warfare to differing degrees. They were never completely absent.

$\begingroup$The issue with other armies not wanting to fight women is real. ISIS is having trouble combatting an all woman platoon that's being fielded against them. Somehow, within the ISIS ranks, the rumor got spread that if you get killed by a woman in combat, you dont' get to go to heaven. This rumor has done serious damage to morale when facing these women.$\endgroup$
– Cort AmmonMay 24 '17 at 17:39

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$\begingroup$"One could argue that young men make good enlisted soldiers because they will take stupid risks" one could more easily argue that that's why they would make worse enlisted soldiers. Battles are rarely won by taking stupid risks. More often they're won through thoughtful tactics and disciplined soldiers.$\endgroup$
– apaulMay 25 '17 at 0:26

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$\begingroup$@apaul34208, discipline and thoughtful tactics are extremely important for the people making the decisions. Once those decisions are made, a swarm of testosterone-fueled idiots are quite effective at carrying them out.$\endgroup$
– MarkMay 25 '17 at 1:30

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$\begingroup$@Mark Just sayin that stupid risks cost lives... In general you should want your soldiers professional and on point.$\endgroup$
– apaulMay 25 '17 at 1:53

$\begingroup$Study the history of the Greek island of Lesbos. I believe that, at one time, they had an army entirely of women. Not very recent, though.$\endgroup$
– user6030May 25 '17 at 2:28

Wow! So many answers without mentioning any of the positives that women bring to the table. To be clear, there are feminine men and masculine women and this answer deals just with the advantages of typical and stereotypical women.

Endurance

Many answers have claimed without justification that women have less endurance than men. The truth is, women have plenty of endurance for the purposes of military activities. In fact, women hold all of the records for super long distance swimming.

Risk Taking Behaviors

Since women tend to take fewer risks, one would expect said fighting force to more rapidly evolve tactics that involve avoiding stupid risks, much as modern (after 2000) warfare is much less risky than its World War era counterpart.

Culture

Military culture has long suffered from toxic masculinity. There are real positives when soldiers obey without question, but creating that outlook is often just a high stakes power struggle. One might expect more good ideas to filter up the ranks in an all-female military.

Equipment

Smaller soldiers need smaller boots, smaller flak jackets, smaller weapons, smaller meal portions and smaller camp accouterments. The idea that a military wouldn't right-size their equipment for their soldiers is ludicrous. Fewer materials means lower costs, so each soldier will be able to travel just as far or further for a marginally lower logistical cost.

War by Other Means

War is kinetic diplomacy. If a country is more worried about its daughters going into battle than it was about its sons, one would expect the balance between diplomatic, espionage and military spending to find a more intelligent distribution.

Babies

Every military has a minority of war fighters and a majority of medical, administrative, logistical and research personnel. There's no reason that soon and recent mothers cannot carry out lower risk tasks during the 18 months per child that a pregnancy takes.

$\begingroup$"There are real positives when soldiers obey without question, but creating that outlook is often just a high stakes power struggle." This seems to be a complete no-sequitur (masculinity does not equal obedience without question - men have been the instigators of a vast number of changes in history), and is also very, very unlikely to be the reason for "command and control" style management in the military. To paraphrase a co-founder of Stack Overflow, soldiers are taught to obey without question so they will run at the enemy in a minefield. If you don't do that, you all die.$\endgroup$
– Robert GrantMay 24 '17 at 21:30

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$\begingroup$you should probably add to your risk taking section that women aren't expendable. every generation has a surplus of men, and you can lose 10-20% without effecting birth rates. that is definitely not true of women.$\endgroup$
– james turnerMay 24 '17 at 23:20

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$\begingroup$@RobertGrant Non-sequitur. Thanks for the feedback. It sounds like you think the military's command and control style is because obedience saves lives in war. I basically agree. The gap between us here is whether and how you get people to unquestioning obedience. It's been a long time since an American force charged into a minefield, and I expect the utility of that style of warfare is basically antiquated. If you don't see the masculinity in how we've traditionally gotten to unquestioning obedience, I probably can't convince you.$\endgroup$
– user121330May 24 '17 at 23:32

$\begingroup$@jamesturner If I were the leading answer, I'd feel pressure to be more comprehensive. As is, I just want to outline some of the positives that women bring to a military force. Birth rates (which are now greatly diminished because most children live to maturity, and may increase per female in the event of a female population decrease) don't seem like a positive unless your primary goal is peace (laudable and I agree, but probably not a positive for OP or all readers).$\endgroup$
– user121330May 24 '17 at 23:38

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$\begingroup$Concerning "War by other means": If both involved countries are more worried about sending in daughters instead of sons, and the second country simply fields men instead of women, then the first country has already a bad start into the war.$\endgroup$
– arc_lupusMay 25 '17 at 11:31

Looking at the physical differences outlined here, men are around 30% stronger than women and have better endurance and physical strength. The military implications of these revolve around 2 main facets:

1: Equipment

The average weight of military gear is around 100 pounds. With proper training, soldiers are able to carry this weight without too much difficulty, however if there are limitations to the strength of your soldiers the mobility of units would have to be greatly decreased.

2: Combat Capabilities

Since women have shorter endurance, the amount of time they would last at an appropriate physical peak during combat is shorter as well. As such, engaging in long skirmishes is not ideal.

Ideas:

My thought would be a military comprised of all female troops would be similar to the Viet Kong in their Guerrilla tactics. This website shows that there have been groups of female soldiers employed to mainly surprise enemy forces, and in my opinion small, mobile groups of soldiers that harass more than attack is the best way to implement an all female military.

$\begingroup$As soon as a place starts using language like, "Although many feminists cannot face this fact..." I no longer trust them; they're politically baiting people, not providing research-based facts. The linked source also doesn't cite its sources, just states a list of things on the assumption that we'd just believe it.$\endgroup$
– AzuaronMay 24 '17 at 17:26

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$\begingroup$Mobility need not be decreased either. They could either carry less or have lighter equipment or divide the labor amongst more soldiers. Also, training can increase endurance. I'm a relatively physically fit male, but I wouldn't stand a chance running a marathon, but plenty of women run every year. This might be more of a selection criterion thing.$\endgroup$
– ozoneMay 24 '17 at 17:28

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$\begingroup$@ozone As a general principle in the military, we already remove every single ounce we can,because weight makes you slow. Team sizes are chosen because they are the sizes that work.$\endgroup$
– Cort AmmonMay 24 '17 at 17:36

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$\begingroup$@ozone Sorry, I meant for the same amount of gear, you would be less mobile. Hence why I suggested guerrilla tactics, which tend to utilize less gear!$\endgroup$
– Sam WorrodMay 24 '17 at 17:48

Impact of Size Differences

Women over 18 are generally shorter than men of the same age. This can vary significantly by region and ethnicity. In the US and UK, men average about 175 cm or 5 ft 9 in tall, while women average 161.8 cm or 5ft 3.5 in tall. In the People's Republic of China, men average about 167 cm (5ft 6in) while women average 155.8 cm (5ft 1.5 in).

Men are taller on average than women by 5.5 inches in the US/UK and by 4.5 inches in China.

The size of warfighters is a significant factor in the design of vehicles, lodging, and equipment.

Having smaller warfighters would make some things more difficult for manufacturers: for example, consider the height of a truck's running board from the ground; for vehicles with large tires and tall ground clearance, the running board or a ladder attachment may need to be lowered to allow shorter warfighters to reliably embark/disembark the vehicles. Along the same vein, assumptions about soldier carrying capacity when it comes to equipment may need to be adjusted downward.

On the other hand, smaller warfighters means you can reduce the size of the cab or increase the number of troops carried, which could have a cascading effect along the entire transportation supply chain (trucks can carry more troops, ocean-going vessels can carry more trucks).

Of course, within any population there's plenty of deviation from the baseline average. You could decide that the military retains some sort of size/strength standards that military personnel must meet, rendering such concerns immaterial (but introducing a new concern: a smaller recruitment pool).

Impact of Psychological Differences

There are significant psychological differences between men and women on average, but it's unfair to make a sweeping statement about psychological differences between every man and every woman. The differences may stem from any of genetic, hormonal, developmental, and social/cultural pressures.

Research suggests that women are more empathic and more emotional than men in general. (Some research argues that women are simply more emotionally expressive rather than more emotional, so this science is certainly not settled.) It also suggests that they are less likely to display aggression directly.

If women in general are more empathic, a female-directed military may be inclined to avoid conflict and pursue diplomatic solutions, but this relies upon the specific women with decision-making authority having both greater empathic perception than their male counterparts and having some means of applying their empathic perception to their (potentially faceless) enemy. In all likelihood, the impersonal and weighty justifications for engaging in modern war would hold the same sway, regardless of whether it's a man or a woman who makes the decision.

If women in general are more emotional, including greater capacity for both joy and fear, that could also affect decisions to wage war or initiate conflict. But again, the decision to wage war is often made at a state level so the personal feelings or intensity of feelings held by decision makers may not change their ultimate decisions when faced with the same options and consequences.

If women in general are less directly aggressive, this might actually serve to the advantage of their military in modern large scale warfare, where combat is often impersonal, waged by proxy with bullets, rockets, missiles, and drones instead of in close personal combat with fists, bludgeons, and blades. An indirectly aggressive military might be more willing to embrace asymmetrical warfare, including booby-traps, or strategic maneuvers like cutting off enemy supply lines.

But there are two big caveats with trying to predict the psychological behavior of a military based on its gender composition:

Individual members of the military will deviate from the average. In much the same way that the average soldier will be different from the average man, the average female in the military will not necessarily match the psychological profile of the average female outside the military.

Their behavior will necessarily be informed by both their experience and training. Nobody is naturally an ideal soldier or general; the abilities to fight and lead in a war require the suppression of some instincts and the elevation or acquisition of others.

Any innate psychological differences between the sexes might thus prove insignificant compared to the differences between soldiers and non-soldiers.

$\begingroup$Your information about average height is actually is pretty interesting - the difference between, say, Chinese men and US women is about 2.5 inches, which is much less dramatic and calls into question some of the more forceful assertions that the (average) size difference is significant and limiting problem for soldiers... after all, China has an active military force despite the ~3in difference between their men and US or UK men. It may well make a difference in logistics or tactics or gear, but perhaps not the absolute difference others are predicting.$\endgroup$
– MeghaJul 6 '17 at 4:02

$\begingroup$@Megha Right... and for most militaries, the equipment and vehicles are designed for the warfighters, not the other way around. If equipment sizing mismatches cause inconvenience or otherwise impact mission performance, that just means new or modified equipment is in order; the process of acquiring new equipment and adapting it to the needs of both the warfighter and the combat theater is constantly taking place anyway, regardless of sex.$\endgroup$
– ThriggleJul 6 '17 at 14:06

$\begingroup$Note that women right now operate the exact same heavy equipment at mines or construction sites as do men, without any alterations in vehicle design necessary. You'd be hard up explaining why a dump truck capable of hauling 200 tonnes doesn't have to be changed while a truck carrying two and a half tonnrs does.$\endgroup$
– Keith MorrisonFeb 12 '18 at 3:59

$\begingroup$@KeithMorrison Commercial construction vehicles are designed freely and marketed competitively. Military equipment is designed according to precise contractual obligations. Commercial manufacturers gain a competitive advantage by making their equipment more accessible for more workers. Defense manufacturers worry first about ticking all the boxes specified by the gov't contract, and then about reducing cost or increasing maintainability so that their equipment will be chosen over competitor products. If the contract specified a minimum warfighter size, product designs will reflect the minimum.$\endgroup$
– ThriggleFeb 12 '18 at 16:47

I'm going to take a different approach than most of the other answers here. Given the current trend in warfare towards hardware and away from large ground forces, I would guess that after the initial transition period, things would carry on in much the same direction that they're already moving.

Modern militaries already prize mental aptitude over physical strength. Your ability to operate the technology is way more valuable than your ability to lift heavy objects... More and more combat is being conducted by drones, air power, heavy vehicles, and war ships. While infantry is still used and is still important, it's very rarely used as a front line. Even when it is, combat is rarely if ever hand to hand, it's much more finger to trigger and infantry weapons tend to get lighter and more efficient with each new generation.

"How would a military staffed only with women be different?"

It wouldn't be much different at all in the long run.

Also... A lot of the answers here also seem to suggest that women are less physically capable as a given. I reject that assumption. While men tend to have more upper body strength, women tend to have greater lower body strength. There isn't really that much difference in muscle mass without physical training, it's just placed differently.

$\begingroup$"While men tend to have more upper body strength, women tend to have greater lower body strength. There isn't really that much difference in muscle mass without physical training, it's just placed differently." DIfference between muscle mass and strength. It's why testosterone is so important, and why female athlete's illegally dope with it. Though, given it's a warfare scenario, there's nothing stopping the gov't overseeing a safe steroid program to help women build themselves up to a stronger-than-normal level while they're in service.$\endgroup$
– PhilboMay 25 '17 at 7:58

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$\begingroup$@Philbo: Who needs a "safe" program, when you are in war?$\endgroup$
– arc_lupusMay 25 '17 at 11:32

1

$\begingroup$@arc_lupus surely after service, these women will still want to have a healthy pregnancy. I can't imagine taking male hormone steroids to the absolute limit of their bodies would be conducive to that...and there's no point winning the war if there's no next generation.$\endgroup$
– PhilboMay 26 '17 at 12:36

As also pointed out in apaul34208's answer, despite the fact that on average there are some physiological difference between men and women, nothing would fundamentally change because of this difference. We need to keep in mind here that most people recruited in the army (males or females) are quite far from their theoretical top fitness level, and it's only at this top level that differences between males and females are readily apparent. Also, we need to consider that the average fitness level of army recruits has been steadily declining, particularly in the US. But despite the fact that the US is the most physically unfit nation of the developed World, the US army is still the most powerful army of the World.

The physical fitness requirements for women are set lower than for men, but this has to do with the drive to get more women recruited into the army. As we can see here, the standards for men are quite low. E.g. a minimum of 49 pushups in 2 minutes with 80 the recommended number is not a lot, my grandfather could do a limitless number of pushups at a fast rate at the age of 80 (with well enough developed arm muscles you'll pass the endurance threshold where you don't need to stop anymore). The cardio-fitness standards are not set to be at a rigorous level either. Take e.g. the 40 minutes time limit for the 5 mile run, that's just over 12 km/h for 40 minutes and that's well below my training speed at which I run every day for more than an hour. In Norway there exists a female only special forces unit, we can read here that the fitness requirements are quite similar to what is required of US males.

I wanted to give some time for answers to percolate before providing any answer of my own, but I'd make a few observations, to ground the analysis, without really resolving some of the trickiest and most interesting parts of the question.

Lots of a military force involves an Air Force and a Navy in addition to the Army. In 2015 in the U.S. military, the force structure was:

Army 491,177

Navy 326,504

Air Force 312,195

Marine Corps 184,587

Coast Guard 40,069

Air Force

In the Air Force, very few personnel actually enter the "battlefield" on a plane, about 95% of the personnel supporting each aircraft are ground crews, where issues of physical strength could be addressed with greater use of machines for lifting and applying strength.

The number of pilots in the Air Force is sufficiently small that your recruits can be very gender atypical, e.g. in emotional and personality character, and still easily to secure in sufficient numbers.

Physical strength and size aren't particularly important in pilots, and the crew portions could be adapted in size for women fairly easily.

The Air Force is currently 19.1% female.

A meaningful subset of the Marines are part of its own internal Air Force to which similar considerations would apply.

Navy and Coast Guard

Many positions in the Navy call for sailors who are actually below average relative to men generally in size, especially submarines. And, relatively few positions on a modern ship call for exceptional physical strength that could not be replaced by more intense use of machines to assist in lifting and moving things. If anything, an all female ship or submarine might more easily achieve a cohesive crew on a long deployment than a ship with only men.

Most of the hand to hand combat training in the Navy is directed at sailors maintain order vis-a-vis other crew members who get unruly, and protecting ships that are docked when it is not necessary to carry lots of heavy gear over long distances on foot.

The U.S. Navy is currently 18.1% female, the U.S. Coast Guard is currently 14.8% female.

Army

While some specialties in the Army fit the traditional stereotypes of what a soldier is, many do not. The U.S. Army is currently 14.2% female.

Lots of soldiers in the Army and lots of Marines (which is currently 7.7% female) have jobs like driving supply trucks, providing medical care, maintaining equipment within forward operating bases, feeding the troops, reviewing intelligence from drones and satellites and troops in the field, and so on. In military lingo they are called "Fobbits" because they work in "forward operating bases".

Certainly resources like artillery have become more accurate and have required less crew support over time, requiring fewer personnel to achieve the same military outcomes.

Another role that was traditionally in the front lines and considered to require physical traits associated with men was operating a tank, even though there were maximum personnel size limitations on tanks. But, the number of tanks in the active duty force has declined greatly, because they have become less militarily useful in modern conflicts, and the tanks that remain have become more automated. Many proposals to make tanks even more automated have been rejected because they weren't a priority, but could be adopted in an all female force.

New positions like drone operators also don't have very gendered demands on personnel. Neither do some quite front line positions like helicopter operators.

Certainly, positions like infantry and special forces would be very strongly impacted, and how those posts in the military would change is very notable. But, those positions are a minority of the modern military, and the changes would be far less dramatic than they were in the days when infantry fought with swords rather than firearms.

Analysis

If one assumes that the Air Force, the Navy, the Coast Guard, and the aircraft operating part of the Marines won't be much different, those components of the military, which make up about half of the U.S. military personnel, wouldn't change very much in character or capabilities.

The Army and Marines would certainly be impacted more, but probably only about 1 in 3 members of those forces would be in the kinds of positions that would be impacted very much. Perhaps up to 250,000 personnel out of almost 1,355,000, or about 18% of the force would have strongly impacted by the transition in how they could or would operate.

Thus, about 82% of the force wouldn't change very much, while about 18% of the force would change a lot in some of the ways discussed in other answers. How that 18% would change is very interesting, but one shouldn't overstate how representative that portion of the force is to the entire military force either.

Transition Period Duration

There would have to be a transition period during which men were phased out of the military and women were phased in, because lots of military skills can only be learned by doing under the supervision of people who know those skills.

But, this wouldn't take terribly long because the military is constantly cycling through personnel. Much of the active duty force serves for four to eight years before returning to civilian life, ten years would be longer than average, and twenty years is about as long as a military career gets.

So, over twelve to sixteen years, a very large part of the transition could be completely relatively seamlessly, without catastrophic loss of skill sets limited to experienced veterans. If there were a greater rush, an eight to ten year transition could still be manageable although it would carry higher costs particularly in the loss of skills at higher ranks where personnel turnover is not as rapid.

$\begingroup$While women could easily take on the role of flying helicopters and larger planes, would they be able to deal with fighter planes? The Air force has that g-force test that involves locking all their muscles out - considering the low number of men fit enough and genetically able to pass that test (it involves contracting a lot of muscles to stop all the blood rushing out of the brain while trying to breathe through a closed glottis through 8Gs), could a woman pass? If not would it mean the country giving up air superiority?$\endgroup$
– PhilboMay 25 '17 at 8:07

2

$\begingroup$A biased sample returns biased results. Say there are twelve positions available. If you test a thousand men and ten get through, then test fifty women and two get through, you get your twelve with a 5:1 ratio. But if you include the women who drop out for totally irrelevant reasons (like the intra-military rape rate, or the societal deprivation of women encouraged to enter military service) then the twelve could easily become 1:1 or overbalanced in favour of women before even testing equal numbers.$\endgroup$
– NijMay 25 '17 at 8:39

1

$\begingroup$@Philbo Have those tests been done on women? Is there evidence that extreme outlier women are more vulnerable to g-forces than extreme outlier men? If so, that would be good to include in an answer. If not, what physiological evidence is there that this is the case? The kind of physical ability involved in a g-force stress is quite different from the kind of physical ability involved in, e.g., carrying 50 kg of gear.$\endgroup$
– ohwillekeMay 26 '17 at 19:19

since women are shorter, slower and weaker than men, they would avoid any confrontation on foot. basically, infantry would be a tiny group of unusually large and exceptionally well trained women.

since women are less expendable than men, trade-offs between risking lives and risking equipment would tend more towards the safety side of the equation at the expense of much larger equipment budgets. although, this has been happening naturally for decades as we have become wealthier. also, the age limits would be raised (both lower and upper) in order to avoid killing off women before they produce baby taxpayers.

$\begingroup$Who said that women were less expendable than men in this culture? If there are almost no men left then those who are left are much less expendable than all the women. When you have a herd of 50 cows and 1 bull which individual is the most expendable?$\endgroup$
– Rick RykerMay 27 '17 at 5:31

$\begingroup$@RickRyker when answering questions in world building i assume we are talking about normal human biology unless otherwise noted.$\endgroup$
– james turnerMay 30 '17 at 15:10

In general, I would expect any country which relies on female infantry troops to be several times more likely to be the subject of aggression than one with a traditional, male infantry. Countries without unfriendly neighbors (Australia, France, ...) and without significant internal unrest would be little affected, with more wealthy nations (more mechanized, more high tech) virtually unaffected, and the less wealthy nations requiring some adjustments in the mix of mechanized and unmechanized infantry. Countries with internal unrest would be far more likely to have their governments overthrown. Countries with unfriendly neighbors would have to spend more on their military, if they had enough time. They'd need more troops, and more effective weapons to counteract the low regard the other nations had for their fighting forces. Problem with this answer is the question. It is obviously absurd to think that the cause of the change doesn't matter. Of course it does! The culture the army is recruited/conscripted from matters enormously. Few cultures expect women to be as physical or as aggressive as males. This matters in determining how aggressive unit tactics can be. We can only speculate, without evidence. The fact that no known nation has ever fielded such a force is neither proof of the hypothesis that female force will be 100x as likely to cut and run as a male force but it certainly doesn't support the hypothesis that such a force will be 100x less likely to fold like a house of cards. There may or may not be a significant biological/physiological difference between the way groups of men and of women behave. Jury is out, but I doubt you'd find many people holding the latter pov, while many hold the former. The one key point is that there are a LOT of women between 18 & 26 that are mothers. I believe they will be LESS willing to leave their children, and less willing to risk their lives for a "greater good" than young men of the same age. It's just a guess, but certainly the proportion of the population that qualifies to get into the military would drop precipitously, and I'd guess the military would have to lower its standards to compensate.

$\begingroup$What about a culture that has a very high ratio of women to men (remember we had to field an entire army of women because ... of hand waved reasons ... which most likely result in such a high ratio) where the right to breed with this limited number of men is dependent on the successful completion of a military tour of duty? We have had cultures where the men to women ration was 3:1, so men were allowed to have up to 3 wives but could not marry until they came back from a successful mission, where such missions had an unusually high death rate.$\endgroup$
– Rick RykerMay 24 '17 at 20:40

$\begingroup$I would not be surprised at all if the change had a real and significant impact, and certainly the premise of the question is not that an all female force would necessarily be militarily superior or even equal. It is safe to assume that the reason for the change isn't because this country thinks that men are inherently worse fighters. But, this said, the magnitude of the change and they way organization and strategy might change to reflect the change, is non-obvious and interesting to explore.$\endgroup$
– ohwillekeMay 24 '17 at 22:43

We are talking about war here.
War is a beast, and a black hole of human nature.

My perspective may be different, and harsh, and more.

If that happened in hundreds or thousands of year ago.
This action just "inspires" enemies to capture as many captives as they can.
Think of the Romans abducting foreign tribe females at the beginning of Roman history. I forget the exact event but it is documented in the book Challenge of the West when the author talks about Rome. You just "offered" women in troops.

War is not romance; it is all about killing, rape, slavery and such.

And if it happened nowadays, the situations have changed a lot, so it is unlikely to be a solid statement that such action will yield a lot of difference in combat capability.

But it does not change the nature of war. The black nature of war allows the winner to do whatever they want to losers.

$\begingroup$Certainly war is hell. But, firearms and missiles tend to be "equalizers". Physical might mattered immensely in Roman warfare with spears and swords and longbows. It matters letter in 2017. I'm not asserting that physical might is irrelevant. But a woman with an assault rifle and a flak jacket is much more equal of an opponent for a man similarly equipped than a woman with a swords and shield is to a man with a sword and shield.$\endgroup$
– ohwillekeMay 26 '17 at 19:23

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